•High magnetic field and high plasma density tokamak with SOL decay length close to ITER and PB/qAR ratio 70% of ITER.•Closed divertor that allows snowflake divertor configuration.•Ohmic losses in ...magnets reduced via cryogenic cooling of Cu coils to liquid nitrogen temperatures.•Operation of the first wall at 300°C.•Auxiliary plasma heating systems: 4MW NBI with variable injection geometry, 4MW ECRH using ITER-like gyrotrons.
The paper describes the conceptual design of the COMPASS Upgrade (COMPASS-U) tokamak which represents a compact, medium-size, high-magnetic-field and high-density device with a flexible set of poloidal field coils for generation of single, double null and snowflake configurations. In addition, COMPASS-U will be equipped with a closed divertor, which will be operated at high plasma and neutral density and with high optical opacity similar to future reactors. COMPASS-U is capable of addressing some of the key challenges in the field of the plasma exhaust physics, reactor-relevant edge plasma physics, advanced confinement regimes, advanced magnetic configurations and materials for next-step devices. The conceptual design of the individual COMPASS-U systems is presented with emphasis on magnets, support structure and power supply system enhancement.
•Main constraints influencing the conceptual design of diagnostics for COMPASS-U were identified.•Diagnostic solutions for the hot vacuum vessel, high plasma densities and high heat flux densities ...are proposed.•Spatial constraints at COMPASS-U are reviewed and possible solutions indicated.
COMPASS-U, a high magnetic field tokamak with hot walls, will be designed and built at IPP Prague. Unique features of this new device bring noticeable constraints and requirements on plasma diagnostics, which make their development highly demanding. In this paper, the main expected constraints influencing the conceptual design of diagnostic tools for COMPASS-U (high temperature of the vacuum vessel, high plasma density, high heat flux density, strong auxiliary plasma heating, spatial constraints, liquid metals in the divertor) are reviewed and possible solutions are indicated.
•Li-BES detection system on the COMPASS tokamak is optimized observation system with high temporal resolution.•High sensitivity to low level light fluctuations.•Optics and detectors with electronics ...are placed in thermally stabilized compact box.•Fast deflection system allows us to measure background corrected electron density profiles on microsecond time-scale.
A new Li beam emission spectroscopy (Li-BES) diagnostic system with a ∼ cm spatial resolution, and with beam energy ranging from 10keV up to 120keV and a 18 channel Avalanche photo diode (APD) detector system sampled at 2MHz has been recently installed and tested on the COMPASS tokamak. This diagnostic allows to reconstruct density profile based on directly measured light profiles, and to follow turbulent behaviour of the edge plasma. The paper reports technical capabilities of this new system designed for fine spatio-temporal measurements of plasma electron density. Focusing on turbulence-induced fluctuation measurements, we demonstrate how physically relevant information can be extracted using the COMPASS Li-BES system.
Abstract We report on the first experimental observation of a spontaneously formed transport barrier in the tokamak with a circular configuration in helium plasmas. There was no external polarization ...of the plasma by electric field or other technique to form the barrier as it is typically used in tokamaks with circular plasma. In general, the transport barriers play an important role in plasma confinement especially in tokamaks with divertor configuration. In our experiments, we clearly observe distinct characteristics of a transport barrier, including a steep gradient of the electron temperature and an enhanced radial electric field along with the change in the plasma potential, floating potential, and electron temperature fluctuation. The electron temperature and the plasma potential are obtained by a combination of the ball-pen and Langmuir probe measurements with high temporal resolution on a shot-to-shot basis. This first experimental observation of the spontaneously formed transport barrier might bring new possibilities to obtain a fusion-relevant study of the edge plasma parameters and transport in helium plasmas even on small tokamaks.
This article presents a basis for the material selection of toroidal field coils of COMPASS-U, a medium size tokamak currently under construction. The main focus is given to a 0D model which produces ...temporal evolution of toroidal field coil parameters (e.g. voltage, temperature, energy) during a plasma discharge based on the specification of the coils, materials and power supply system. Linkage of these parameters, together with the design requirements of the tokamak, allows the reduction of design parameters space. The model was used for the selection of copper alloy candidate materials for the coils. Mechanical and electrical material tests and results from the model used to select material candidates are presented.
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•Toroidal field coils provide 5T at a major radius of 0.894m for at least 1s.•0D numerical model was used in material selection process.•Electrical and mechanical tests of materials at room and cryogenic temperatures.
This paper summarizes the status of the COMPASS tokamak, its comprehensive diagnostic equipment and plasma scenarios as a baseline for the future studies. The former COMPASS-D tokamak was in ...operation at UKAEA Culham, UK in 1992-2002. Later, the device was transferred to the Institute of Plasma Physics of the Academy of Sciences of the Czech Republic (IPP AS CR), where it was installed during 2006-2011. Since 2012 the device has been in a full operation with Type-I and Type-III ELMy H-modes as a base scenario. This enables together with the ITER-like plasma shape and flexible NBI heating system (two injectors enabling co- or balanced injection) to perform ITER relevant studies in different parameter range to the other tokamaks (ASDEX-Upgrade, DIII-D, JET) and to contribute to the ITER scallings. In addition to the description of the device, current status and the main diagnostic equipment, the paper focuses on the characterization of the Ohmic as well as NBI-assisted H-modes. Moreover, Edge Localized Modes (ELMs) are categorized based on their frequency dependence on power density flowing across separatrix. The filamentary structure of ELMs is studied and the parallel heat flux in individual filaments is measured by probes on the outer mid-plane and in the divertor. The measurements are supported by observation of ELM and inter-ELM filaments by an ultra-fast camera.
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